Mock prompt bank

How to use

105 prompts: 40 system design, 25 AI system design, 15 low-level design, 25 behavioral/Staff. Each is tagged with difficulty and links to prep pages where they exist. Difficulty: M = Senior-bar standard · H = Senior-hard / Staff standard · XH = Staff/Principal (ambiguous, multi-team, migration or deep distributed theory). Staff twist: for any prompt, add one of: "How would you roll this out across 100 teams?", "Cut the cost by 50%", "Now make it multi-region active-active", "You have 2 engineers and 3 months — what do you build first?" Use them with a peer, a paid mock, or the AI mock interviewer; score with the rubric.

System design (40)

Classic web-scale

#	Prompt	Diff	Tags	Prep
SD1	URL shortener with custom aliases, expiry and near-real-time click analytics	M	hashing, KV, analytics	case study
SD2	Pastebin with 10 GB/day uploads and expiring pastes	M	blob storage, TTL	storage and CDN
SD3	News feed / timeline for 300M DAU	H	fan-out, ranking, caching	case study
SD4	Chat system (1:1 + groups up to 500, presence, read receipts)	H	websockets, ordering	case study
SD5	Notification system (push/email/SMS, 1B/day, preferences)	M	queues, retries, dedupe	case study
SD6	Typeahead / search autocomplete for 50k QPS	M	tries, caching	search systems
SD7	Web crawler for 1B pages/month with politeness	H	frontier, dedupe, scheduling	data pipelines
SD8	Video upload and streaming platform (YouTube-lite)	H	transcoding, CDN, adaptive bitrate	storage and CDN
SD9	Photo sharing with feed and likes (Instagram-lite)	M	blob, feed, counters	caching
SD10	Google Docs-style collaborative editor	XH	OT/CRDT, presence, consistency	consistency models

Infrastructure and platform

#	Prompt	Diff	Tags	Prep
SD11	Distributed rate limiter across 3 regions for 2,000 services	H	token bucket, consistency	rate limiting
SD12	Distributed key-value store with tunable consistency	XH	replication, quorums, gossip	case study
SD13	Distributed job scheduler (cron at scale, exactly-once execution semantics)	H	leases, idempotency	case study
SD14	Metrics and monitoring system (1M series/s ingest, 13-month retention)	H	TSDB, downsampling	case study
SD15	Distributed message queue / Kafka-lite	XH	log, partitions, ISR	messaging and streaming
SD16	Distributed cache (Redis-cluster-like) with hot-key handling	H	consistent hashing, eviction	partitioning
SD17	Centralised logging platform for 5 TB/day	H	ingestion, indexing, tiering	observability and SLOs
SD18	Feature flag / config service with < 1 s propagation	M	push vs pull, consistency	reliability patterns
SD19	API gateway for a microservices estate (auth, routing, quotas)	H	proxies, authN/Z	load balancing
SD20	Distributed lock service (Chubby/ZooKeeper-like)	XH	consensus, fencing tokens	consensus and Raft
SD21	Blob storage service (S3-lite) with erasure coding	XH	durability, metadata	storage and CDN
SD22	Unique ID generator (Snowflake-like) for 1M IDs/s	M	clocks, coordination-free	scalability fundamentals
SD23	Multi-region active-active user-profile service with DR (RPO 0, RTO 5 min)	XH	replication, failover	multi-region and DR
SD24	Change-data-capture pipeline from 200 Postgres DBs to a lakehouse	H	CDC, schemas, ordering	data pipelines

Transactions, money and marketplaces

#	Prompt	Diff	Tags	Prep
SD25	Payment system for a marketplace with multiple PSPs, ledger, reconciliation	XH	idempotency, double-entry	case study
SD26	Ride hailing / proximity matching (Uber-lite)	H	geo-index, matching	case study
SD27	Ticket booking (concerts) with 1M users at on-sale	H	contention, queues, holds	consistency models
SD28	Hotel/flight reservation system with overbooking rules	H	inventory, sagas	sagas and outbox
SD29	E-commerce order management (cart → order → fulfilment)	M	sagas, events	messaging and streaming
SD30	Digital wallet with P2P transfers and fraud checks	XH	ledger, consistency, risk	payment system
SD31	Stock exchange order matching engine (low latency)	XH	single-writer, sequencing	reliability patterns
SD32	Ad click aggregation with exactly-once counts for billing	H	stream processing, dedupe	data pipelines

Domain / enterprise (logistics flavoured)

#	Prompt	Diff	Tags	Prep
SD33	Real-time container/shipment tracking for 10M active shipments with ETA updates	H	events, geo, fan-out	messaging and streaming
SD34	Global booking platform for a shipping line (capacity, pricing, allocations)	XH	inventory, consistency, multi-region	data architecture
SD35	Event-driven integration hub between 300 partner systems (EDI, APIs, files)	H	integration patterns, schemas	integration patterns
SD36	Multi-tenant SaaS platform with tenant isolation and noisy-neighbour control	H	tenancy, quotas	security and multi-tenancy
SD37	Document management with search, versioning and retention for regulated data	M	storage, search, compliance	search systems

Staff / Principal (ambiguous, organisational)

#	Prompt	Diff	Tags	Prep
SD38	Migrate a 15-year-old monolith (order management) to services without downtime; 12 teams involved	XH	strangler fig, data migration	legacy modernization
SD39	Company has 3 incompatible event platforms after acquisitions; design the convergence	XH	platform strategy, migration	team topologies
SD40	Define API standards and versioning for 400 internal APIs; how do you enforce without blocking teams?	XH	governance, contracts	API contracts and versioning

AI system design (25)

RAG and search

#	Prompt	Diff	Tags	Prep
AI1	Enterprise RAG assistant over 2M documents with document-level ACLs and citations	H	hybrid retrieval, ACL, evals	rag system
AI2	Semantic product search for an e-commerce catalogue of 50M items	H	embeddings, hybrid, ranking	AI search
AI3	Customer-support RAG bot that must never give wrong policy answers	M	grounding, refusal, HITL	rag system
AI4	Multi-tenant RAG platform offered to 500 B2B customers	XH	isolation, cost, noisy neighbour	advanced RAG
AI5	Q&A over contracts requiring multi-hop reasoning ("which customers are affected if port X closes?")	XH	GraphRAG, structured + unstructured	advanced RAG

Assistants and agents

#	Prompt	Diff	Tags	Prep
AI6	ChatGPT-style assistant for 10M users: conversations, memory, file uploads	H	streaming, memory, safety	chat assistant
AI7	Multi-agent platform for 50 internal teams calling internal APIs	XH	tool registry, identity, HITL	agent platform
AI8	Operations copilot that triages exceptions and takes approved actions (capstone)	XH	orchestration, evals, guardrails	capstone
AI9	Coding agent / automated code-review bot for 2,000 repositories	H	sandboxing, context, evals	coding agent
AI10	Email/inbox agent that drafts and sends replies on a user's behalf	H	lethal trifecta, approvals	guardrails and security
AI11	Voice agent for a call centre (sub-second turn latency)	XH	streaming ASR/TTS, latency budget	cost and latency
AI12	Deep-research agent that produces cited reports in 10 minutes	H	planning, parallel tools, verification	multi-agent systems
AI13	Agent memory service shared across products (preferences, facts, episodes)	H	memory, privacy, provenance	memory systems
AI14	Long-running procurement agent that waits days for approvals and supplier replies	H	durable execution, HITL	durable execution

Platform, gateway, evaluation

#	Prompt	Diff	Tags	Prep
AI15	Multi-tenant LLM gateway for 40 teams and 5 providers with budgets and chargeback	H	routing, quotas, observability	LLM gateway
AI16	LLM evaluation and observability platform for the whole company	XH	offline/online evals, judges, tracing	evaluation platform
AI17	Prompt management and experimentation platform (versioning, A/B, rollback)	M	config, experimentation	LLM observability
AI18	Guardrails service used by every AI product (input/output/tool policies)	H	classifiers, latency, policy	guardrails and security
AI19	MCP server registry and gateway for an enterprise (discovery, auth, audit)	XH	MCP, OAuth, governance	MCP

Serving, documents, cost

#	Prompt	Diff	Tags	Prep
AI20	LLM inference platform for 3 open-weight models at 5k req/min	XH	GPUs, batching, autoscaling	LLM serving platform
AI21	Intelligent document processing for 1M trade documents/month	H	OCR, extraction, HITL review	document processing
AI22	Cut LLM spend of an existing product by 60% without quality loss	H	routing, caching, distillation	capacity and cost planning
AI23	Fine-tuning platform for internal teams (data, training, eval, deploy)	XH	LoRA, eval gates, registry	fine-tuning
AI24	Recommendation system for a marketplace home feed (classic ML + LLM features)	H	two-tower, ranking, features	recsys basics
AI25	Your company wants "AI in every product" in 12 months: design the shared platform and operating model	XH	strategy, platform, governance	AI-native architecture

Low-level design (15)

#	Prompt	Diff	Focus	Prep
LLD1	Parking lot (spots by size, tickets, pricing) + change request: EV charging with reservations	M	modelling, strategy pattern	design patterns
LLD2	LRU cache with TTL, thread-safe	M	data structures, locking	concurrency and LLD
LLD3	Rate limiter library (token bucket, sliding window) pluggable per key	M	strategy, concurrency	rate limiting
LLD4	Elevator control system for a 40-floor building with 6 elevators	H	state machines, scheduling	design patterns
LLD5	In-memory pub/sub message broker with topics, consumer groups, at-least-once	H	concurrency, queues	concurrency and LLD
LLD6	Splitwise-style expense sharing with debt simplification	M	modelling, graph	SOLID and refactoring
LLD7	Library management / book lending system	M	modelling, invariants	DDD tactical
LLD8	Shipment lifecycle state machine with guards, side effects and audit	H	state pattern, events	DDD tactical
LLD9	Thread pool / bounded executor with graceful shutdown	H	concurrency primitives	concurrency models
LLD10	Job scheduler (cron expressions, retries, priorities) in-process	H	heaps, time, concurrency	heap
LLD11	Logging framework with levels, appenders, async flushing	M	chain of responsibility, observer	design patterns
LLD12	Chess or tic-tac-toe game engine with undo	M	command pattern, validation	design patterns
LLD13	Tool-calling agent runtime: tool registry, schema validation, retries, budgets	H	interfaces, typing	tool calling
LLD14	Circuit breaker + retry with backoff library	H	state machine, concurrency	reliability patterns
LLD15	Vending machine / payment kiosk with multiple payment methods	M	state pattern	design patterns

Behavioral / Staff (25)

Prep: behavioral interviews. Answer in STAR(L): Situation (< 45 s), Task, Actions (with "I"), Result (numbers), Learning.

Scope and impact

#	Prompt	Diff	Signal tested	Related
B1	Tell me about your highest-impact work in the last 3 years.	H	scope, impact	Staff archetypes
B2	Describe the most technically complex project you led end-to-end.	M	technical depth, ownership
B3	Tell me about a technical strategy or vision you created for multiple teams.	XH	strategy, alignment	technical strategy
B4	Tell me about a time you identified a problem nobody had asked you to solve.	H	ownership, ambiguity
B5	Describe a time you reduced cost, latency or incidents significantly. How did you measure it?	M	impact, data

Influence and conflict

#	Prompt	Diff	Signal tested	Related
B6	Tell me about a conflict with a peer or another team over a technical decision.	M	conflict, collaboration	influence without authority
B7	Tell me about a time you influenced a decision outside your team without authority.	H	influence	influence without authority
B8	Tell me about a time you disagreed with your manager or a senior leader.	H	courage, judgement	communication
B9	Describe a time you had to get several teams to adopt a standard or platform.	XH	coalition-building	architecture reviews
B10	Tell me about a decision you made that was unpopular.	H	conviction, empathy	decision making

Ambiguity, judgement and failure

#	Prompt	Diff	Signal tested	Related
B11	Tell me about a project that failed or missed its goals.	M	self-awareness
B12	Tell me about a time you were wrong about a technical decision.	H	humility, learning
B13	Tell me about a time you made a decision with incomplete data.	H	judgement, reversibility	decision making
B14	Tell me about a time you killed or significantly changed a project.	XH	prioritisation
B15	How did you handle significant technical debt competing with feature work?	H	trade-offs, business framing	technical debt
B16	Describe a time you balanced speed against quality under a hard deadline.	M	pragmatism

Growing others and org health

#	Prompt	Diff	Signal tested	Related
B17	Tell me about someone you mentored or sponsored into a bigger role.	H	growing others	mentoring and sponsorship
B18	How have you raised the engineering bar beyond your own team?	XH	mechanisms	architecture reviews
B19	Tell me about a time you gave difficult feedback to a senior engineer.	H	candour
B20	Describe how you onboarded into a new, complex domain quickly.	M	learning

Operations, AI era and motivation

#	Prompt	Diff	Signal tested	Related
B21	Describe an incident you led. What changed afterwards?	H	incident leadership	incident leadership
B22	How have you introduced AI tools or AI features into a team responsibly? What went wrong?	H	AI-era leadership	AI-era leadership
B23	Tell me about a design doc or RFC you wrote that changed direction after review.	M	written communication	design docs and RFCs
B24	What kind of Staff engineer are you (archetype), and what work do you avoid?	H	self-knowledge	Staff archetypes
B25	Why this role, and what would you do in your first 90 days?	M	motivation, planning

Story bank coverage

Map your 8–10 strongest stories against B1–B25. Each story should cover 3+ prompts. Any prompt with no story → write one before the next checkpoint.